This invention relates to insulin administrating apparatus of the type which comprises a portable proportioning dispenser with a syringe for injecting the remedy into the patient through a needle being steadily introduced subcutaneously, and means adapted to produce a programmed and controlled forward movement of the syringe plunger.
Known are apparatus of this type, wherein the syringe plunger forward movement is produced by means of a pusher with a nut screw threaded seat wherein is engaged a matching threaded shaft rotatively driven, at programmed intervals, by an electric motor operated through an electronic control circuit.
The dosage occurs by controlling or adjusting the shaft rotation by subdividing it into basic angular ranges of preset amplitude, e.g. 90.degree.. Moreover, upon completion of each angular rotation, the rotary movement is discontinued and resumed after a programmable time lapse which establishes the dosage intervals.
The power supply to the motor is interrupted by the action of sensors sensing the shaft angular position and reset by an electronic timer comprising a driving oscillator and divider which sends the enabling command to the power supply as a preset number of pulses from the oscillator are counted thereby by varying the oscillator frequency, the rate of operation of the timer is changed. In general, known apparatus of the type specified above comprise two timing rates produced by corresponding oscillator frequencies, or by respective driving oscillators, and means for programming the time duration of the higher timing rate.
The known apparatus hereinabove specified have given satisfactory results but have some drawbacks resulting from the necessity of discontinuous insulin administrations in relation to particular situations of the patient's metabolic cycle.
As in known, in fact, with diabetic patients the necessity of administrating insulin grows with the assumption of meals and the amount varies proportionally with the magnitude of the meal itself.
A prevailing medical trend recommends the assumption of the extraordinary dose ahead of meals in a single solution. For this purpose the prior apparatus of the type specified are provided with devices for advancing the syringe pusher which are controlled each time by the patient for the administration of the extraordinary dose. A proposed device comprises a manually controlled, suitably scaled, screw which acts on the threaded shaft to produce the forward movement of the syringe pusher while excluding the motor action. Another device avails itself of a push-button which, when actuated directly by the patient, activates the motor; for each actuation of the push-button there corresponds a basic angular rotation range of the pusher-moving threaded shaft.
Both these systems have proved to be impractical but above all unreliable in relation to the excessive care that the patient is to pay in controlling the screw, or respectively the pushbutton, to achieve a precise delivery of the prescribed dose.
In particular with the motor pushbutton actuating system, since each actuation results in a basic angular rotation range, the number of the pushbutton actuations may be very high, e.g. 20 actuations. It will be appreciated that such a circumstance may originate even appreciable counting errors and be inconvenient and annoying for the patient.